Why is Vit D done?

To determine vitamin D deficiency when calcium level is low or a person has symptoms of vitamin D deficiency such as bone malformation in children (rickets) and bone weakness, softness, or fracture in adults (osteomalacia).

Before starting therapy for osteoporosis.

To monitor the adequacy of treatment in patients who are receiving Vitamin D supplements, calcium, phosphorus, and/or magnesium supplements.

To diagnose/monitor problems with the parathyroid gland functioning since the parathyroid hormone (PTH) is essential for vitamin D activation.

To monitor the health status of individuals with diseases that interfere with fat absorption, such as cystic fibrosis and Crohn’s disease and in patients who have undergone gastric bypass surgery.

What does Vit D Measure?

Vitamin D Test measures the levels of Vitamin D in the blood. Two forms of vitamin D can be measured in the blood, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D. The 25-hydroxyvitamin D is the major form found in the blood and is the relatively inactive precursor to the active hormone, 1,25-dihydroxyvitamin D. Because of its long half-life and higher concentration, 25-hydroxyvitamin D is commonly measured to assess and monitor vitamin D status in individuals.

The 25-hydroxyvitamin D test is done to determine the level of Vitamin D in your blood, whether it is low or higher than normal. Low levels can be seen if a person is not getting enough exposure to sunlight or enough dietary vitamin D to meet his or her body's demand or if there is a problem with its absorption from the intestines (cystic fibrosis, crohn’s disease, who have undergone gastric bypass surgery). Sometimes, medicines used to treat seizure (Phenytoin) can cause Vitamin D deficiency by interfering with transformation to 25-hydroxyvitamin D in the liver. Severe liver and kidney diseases can also cause vitamin D deficiency. High levels reflects excess supplementation of the vitamin.

Interpreting Vit D results

Interpretations

Low vitamin D level than normal reference range indicates vitamin D deficiency which can be because of less sun exposure, dietary deficiency or due to decreased absorption from the intestine.

High vitamin D level than normal reference range indicates vitamin D intoxication and is usually due to excess supplementation of the vitamin.

Range:

The normal range of vitamin D is measured as nanograms per milliliter (ng/mL) or nmol/L and can vary from lab to lab.

Level

Reference range (ng/mL)

Deficiency

<20

Insufficiency

20-29

Sufficiency

30-100

Toxicity

>100

Note:

· There can be seasonal variation in 25 (OH) vitamin D level, with values being 40-50% lower in winter than in summer. It is also influenced by sunlight, latitude, skin pigmentation, sunscreen use, and hepatic function.

Frequently Asked Questions about Vitamin D (25-OH)

Q. How is this test performed?

This test is performed on a blood sample. A syringe with a fine needle is used to withdraw blood from a blood vessel in your arm. The healthcare provider will tie an elastic band around your arm to make the blood vessels swell with blood. This makes it easier to withdraw blood. You may be asked to tightly clench your fist. Once the veins are clearly visible, the area is cleaned with an antiseptic solution and then the needle is inserted into the blood vessel to collect the sample. You will feel a tiny pinprick during the procedure. Blood sample once collected will then be sent to the laboratory.

Q. Is there any preparation required before the test?

Inform the doctor about the medications you may be taking. No other specific preparations are usually required before this test.

Q. What is osteomalacia?

Osteomalacia is softening of the bones due to demineralization (the loss of mineral) and most notably by the depletion of calcium from bone. It is a characteristic feature of vitamin D deficiency in adults. Osteomalacia can also be caused by poor dietary intake or poor absorption of calcium and other minerals needed to harden bones.

Q. What are the sources of Vitamin D?

Vitamin D is derived from endogenous sources and exogenous sources. Endogenous sources are produced in our body when our skin is exposed to sunlight. Whereas, exogenous sources can only be derived from other sources, as they are not produced in our bodies. Dietary sources of vitamin D include fish, eggs, fortified dairy products, and dietary supplements.

Q. What does the Vitamin D test result mean?

A below normal level indicates vitamin D deficiency, it can occur in conditions such as lack of exposure to sunlight, dietary deficiency of vitamin D, liver and kidney diseases, poor food absorption in cystic fibrosis and Crohn’s disease, and in patients who have undergone gastric bypass surgery. Along with that, using certain medicines such as phenytoin, phenobarbital, and rifampin, etc. can cause vitamin D deficiency. These reduced levels of vitamin D can also be observed in infants who only feed on breast milk. Such infants can be given formula milk, as it is fortified with vitamin D. An increased level of vitamin D is called hypervitaminosis D or vitamin D toxicity. This is most commonly caused by taking too much vitamin D and can result in increased calcium levels in the body (hypercalcemia). It can also cause kidney and blood vessel damage.

Q. Who should be tested for Vitamin D?

Vitamin D 25 (OH) should be tested in individuals who are undergoing therapy to prevent or treat osteoporosis, patients having signs and symptoms of low calcium level (hypocalcemia) or high calcium level (hypercalcemia). It should also be done in patients with cystic fibrosis, Crohn’s disease, and with gastric bypass surgery, patients receiving vitamin D therapy who do not demonstrate clinical improvement. Along with that, these tests can be done in elderly people, especially those with minimal exposure to sunlight, children and adults with suspected rickets and osteomalacia, respectively, and infants who are exclusively breastfed.

Q. What are the factors which can affect the 25-OH Vitamin D levels?

There can be various factors that can affect 25-OH vitamin D levels, some of them are explained below:
Seasonal variation: Ideally, all samples should be collected in one season. The reason being, there can be seasonal variation in 25 (OH) vitamin D level, with values being 40-50% lower in winter than in summer. This can affect the absorption rate of Vitamin D.
Age: Older adults have a reduced level of 7-dehydrocholesterol, so they cannot synthesize 25(OH) vitamin D. Along with that, the production of active hormone (1,25 dihydroxyVitamin D3) gets reduced by their kidneys.
Skin color: Melanin in the darker skin reduces the ability to produce 25(OH) Vitamin D from sunlight exposure, as it absorbs the sunlight.
Body mass index/nutrition: Obese individuals (body mass index >30 kg/m2) are deficient in Vitamin D, as Vitamin D is fat-soluble. This is because it gets sequestered in the fat and not able to circulate. As a result, the rate of absorption of Vitamin D remains low in obese patients as compared to other healthy individuals.
Certain medicines like phenytoin (seizure drug), phenobarbital, and rifampin, cholestyramine, orlistat, steroids, stimulant laxatives can reduce Vitamin D level.
Other than these, Vitamin D can also get influenced by sunlight, latitude, sunscreen use, and hepatic function.

Q. What are additional tests needed to be performed in case of abnormal Vitamin D test results?

Osteoporosis is a condition of fragile bones with increased susceptibility to fracture. Vitamin D and calcium deficiency are one of the leading causes of osteoporosis. Other risk factors can be genetics, lack of exercise, personal history of fracture as an adult, cigarette smoking, excessive alcohol consumption, history of rheumatoid arthritis, low body weight, and family history of osteoporosis. Usually, osteoporosis does not manifest itself until bone fractures occur. X-rays and bone mineral density test can help diagnose osteoporosis.

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